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Show . . ally diluted, fIred furnaces, oxidant preheaters are not common and the exhaust gases are typIC nI as cleaned, and exhausted with no attempt at energy recovery. Batch preheating for oxyge d g. n fired furnaces is even more attractive than for air/gas fired furnaces because savings are m~ ~ ~n both purchased fuel and oxygen. Figure 3 displays the percentage of furnace input energy os 1 the flue gas as a function of flue gas temperature in an oxygen/fuel fired furnace. The gains in energy utilization through oxygen-fuel combustion, although significant, in most cases do not offset the added cost of the oxygen. Although much work is being done t~ lower the cost of oxygen, present day oxygen costs are equal to or slightly greater than the fue cost for most plants. Technologies are therefore needed to improve the economics of the oxygen-fuel combustion process so that the environmental benefits afforded by this technology can be realized in a cost effective manner, keeping the glass industry competitive. Preheating the incoming raw materials is an excellent way of improving the overall economics of oxygen-fuel melting systems. Even with the 70% reduction in stack gases afforded by oxygen fuel firing, there is still a significant portion of the energy input to the furnace leaving the high temperature stack gases, as shown in Figure 3. Batch and cullet preheating reduces the energy lost via the stack gases by transferring a significant portion of this energy to the incoming raw materials. As can be seen in Figure 4, up to 25% of the required melt energy can be transferred to the batch/cullet in the preheater. Instead of having the raw materials enter the furnace at ambient temperature, they can enter the furnace at up to 1000°F. Above 1000°F, some of the glass forming materials, particularly the cullet, become soft and sticky, making further preheating unattractive due to increased handling difficulties. Figure 5 describes the energy flow which can be acheived with an oxy/gas fired furnace and batch preheating. History of Development The Raining Bed Heat Exchanger was conceived in 1983 under a contract with the Department of Energy to develop heat exchanger technology for the minerals processing industries. It received further development under a contract with the Gas Research Institute (GRI) to develop a cullet preheater which was demonstrated at the Foster-Forbes glass plant in Milford, MA. The Foster-Forbes plant was also the site of a fluidized bed batch preheating project which was performed prior to the Raining Bed Cullet Preheater demonstration. Patents were awarded on the application of the Raining Bed Heat Exchanger for application with glass batch and cullet preheating. These patents are assigned to GRI. The Foster-Forbes Raining Bed Heat Exchanger cullet preheating demonstration was operated for over 1200 hours and preheated over 2000 tons of cullet. Preheater feed rates varied between 20 to 50 TPD and preheated cullet to temperatures ranging from 500 to 700°F. This preheater demonstration was relatively successful but problems with the cullet handling system eventually resulted in a decision to shut down the system. s Most recently, a consortium of organizations have joined together to demonstrate th preheating of glass batch and cullet mixtures with oxygen-gas fired furnaces in two Co . e furnaces. Funding is provided by the Gas Research Institute, the New York State E mmg Research and Development Authority, the New York Gas Group, the U.S. Departm nergy Energy, Coming, Inc., and Praxair, Inc. The goal of this effort is to demonstrate the ent of energy saVI. ng b enef I' ts 0 f preh eatI. ng b atc h an d cu1 e1t m"Ix tures In oxygen-gas furnaces. cost and 2 |
